1. Field of the Invention
The present invention relates to a nozzle touch mechanism of an injection molding machine, configured to prevent a stationary platen from inclining during nozzle touch operation.
2. Description of the Related Art
In a mold clamping mechanism section of an injection molding machine, a stationary platen and a rear platen are connected to each other by a plurality of tie-bars, and a movable platen is disposed between these platens for movement along the tie-bars. Further, stationary and movable mold halves of a mold are attached individually to facing machined surfaces of the stationary and movable platens, whereby mold clamping and opening operations are performed.
Furthermore, an injection unit is advanced and retracted relative to the stationary platen on a machine base, and a nozzle on the distal end of an injection cylinder of the injection unit is brought into close contact with a resin injection port of the stationary platen. In this state, a resin is introduced into the mold through the injection cylinder. A nozzle touch mechanism is provided to bring the nozzle into close contact with or separate it from the resin injection port of the stationary platen. The nozzle on the distal end of the injection cylinder is configured to be pressed against the resin injection port of the stationary platen by the nozzle touch mechanism during continuous molding operation.
FIGS. 11 and 12 are views showing the entire configuration of an injection molding machine comprising a nozzle touch mechanism section. FIGS. 11 and 12 show states where the nozzle is untouched and touched, respectively.
The injection molding machine comprises a mold clamping section Mc and an injection section Mi on a machine base (not shown). The injection section Mi serves to melt a resin material (pellets) by heating and inject the molten resin material into a cavity of a mold 40 (comprising movable and stationary mold halves 40a and 40b). The mold clamping section Mc serves mainly to open and close the mold 40.
The injection section Mi will be described first. A nozzle 2 is attached to the distal end of an injection cylinder 1, and a screw 3 is inserted in the injection cylinder 1. The screw 3 is provided with a resin pressure sensor 5, such as a load cell, configured to detect the resin pressure based on a pressure on the screw 3.
The screw 3 is rotated by a screw-rotation servomotor through a transmission mechanism 6 comprising pulleys, belt, etc. Further, the screw 3 is axially moved by an injection device advancing/retracting mechanism 8. Reference numeral 4 denotes a hopper that supplies the resin to the injection cylinder 1.
The following is a description of the mold clamping section Mc. The mold clamping section Mc comprises a rear platen 31, movable platen 30, tie-bars 32, stationary platen 33 secured on a base structure 9, crosshead 34, and ejector mechanism 35. The rear platen 31 and the stationary platen 33 are connected to each other by the tie-bars 32, and the movable platen 30 is located so as to be guided by the tie-bars 32. The movable and stationary mold halves 40a and 40b are attached to the movable and stationary platens 30 and 33, respectively. If the crosshead 34 is advanced or moved to the right in FIGS. 11 and 12, the movable platen 30 is advanced to close the mold.
The following is a description of the molding operation by means of the injection molding machine. If a movable platen advancing/retracting motor (not shown) is rotated forward, a ball screw shaft 38 is rotated forward. Thereupon, the crosshead 34 threadedly engaged with the ball screw shaft 38 is advanced (to the right in FIG. 1), so that the movable platen 30 is also advanced.
If the movable mold half 40a attached to the movable platen 30 contacts the stationary mold half 40b attached to the stationary platen 33 (or if the mold is closed), a mold clamping process is started. In the mold clamping process, a mold clamping force is generated in the mold 40 by further driving the movable platen advancing/retracting motor forward. Further, the cavity in the mold 40 is filled with the molten resin as a geared motor M1 for injection device advance and retraction of the injection device advancing/retracting mechanism 8, attached to the injection section Mi, is driven so that the screw 3 advances axially.
In a mold opening process, if the movable platen advancing/retracting motor is driven in the reverse direction, the ball screw shaft 38 is rotated in the reverse direction. As this is done, the crosshead 34 is retracted, a toggle mechanism is operated to bend, and the movable platen 30 is retracted toward the rear platen 31. When the mold opening process is completed, an ejector pin (not shown) is pushed out of the movable mold half 40a, whereby a molded article is ejected from the movable mold half 40a. 
If the nozzle touch mechanism in the state of FIG. 11 is shifted to the state of FIG. 12 so that a nozzle touch occurs, a moment equivalent to the product of a nozzle touch force and the distance from the lower surface of the stationary platen to the nozzle center is generated, possibly causing the stationary platen to tilt or overturn.
Japanese Patent Application Laid-Open No. 9-277306 discloses a nozzle touch mechanism configured so that a pair of rotation/linear motion conversion mechanisms are arranged axially symmetrically with respect to the center of an injection unit. In this configuration, the points of action of the respective screw shafts of the rotation/linear motion conversion mechanisms on the stationary platen are made axially symmetrical with respect to the point of action of a nozzle of an injection cylinder, so that the stationary platen can be prevented from being inclined or overturned by a nozzle touch.
In the nozzle touch mechanism described above, the stationary platen can be prevented from inclining or overturning as the point of action of a nozzle of an injection cylinder is made axially symmetrical with respect to the points of action of the respective screw shafts of the rotation/linear motion conversion mechanisms on the stationary platen, but connecting rods may hinder the maintenance of a swivel of the injection unit or the nozzle tip. Since a nozzle touch mechanism section is located near a front plate of an injection molding machine, moreover, the maintenance of a screw joint is not easy.
Furthermore, Japanese Patent Application Laid-Open No. 2001-315157 discloses a nozzle touch mechanism of an injection molding machine, which uses an electromagnet to bring a nozzle into contact with a sprue bushing of a mold by pressure bonding with a predetermined force.
Since this nozzle touch mechanism uses the electromagnet, electric current must always be kept flowing while the force is being generated. If electric power consumption increases or power failure occurs when generation of the force is required, the pressing force of the nozzle becomes so small that a resin inevitably flows out.